1. Field of the Invention
The present invention pertains to improvements in compositions and methods for zonal isolation for vertical, deviated, and horizontal oil and gas wells. The method involves the utilization of universal fluids for providing settable filter cake while drilling and the subsequent in-situ solidification of the universal fluids to compressive strengths well in excess of that required for casing support, zonal isolation, and borehole stability.
2. Description of Prior Art
The general procedure of drilling an oil or gas well includes drilling a borehole using a drilling fluid. Subsequent to drilling the borehole, casing is run into the well preparatory to placing a cement slurry in the annulus between the outside of the casing and the borehole wall. In order to obtain a good cementing job, it is necessary to displace substantially all of the drilling fluid or mud in the annulus with cement. This necessity arises from the fact that undisplaced mud and filter cake become the source of unsuccessful cement jobs since drilling fluids and cements are usually incompatible. Thus, most water base muds will either cause instant setting of the cement or act as a retarder of the cement setting that can adversely affect the strength of the cement. On the other hand, most cements will flocculate and thicken most water base muds. As the cement is pumped out of the bottom of the casing and up the annulus, it may form flow channels through blocking sections of flocculated drilling mud. In addition, undisplaced filter cake can prevent cement from bonding to the formation and becomes the source of the flow channels.
The drilling industry has sought to overcome the above problems by using a variety of techniques to displace the drilling fluid with cement, e.g., utilization of turbulent flow regimes, casing movement (reciprocal/rotation), casing equipment (centralizers, flow diverters, and mud scratchers) spacers and special wash fluids while cementing, but these have had limited success. Even greater cementing difficulties are encountered with high-angle bore holes, with major problems arising in connection with running casing, drilled solids, settling of solids, displacement of mud, centralization of casing, and cement slurry free water. When a poor cementing job results due to these problems, it may be necessary to perforate the casing and squeeze cement under high pressure through the perforations into the annulus and try to fill the zones that were not properly cemented initially. Frequently, squeeze cementing is not successful, and such failure may eventually lead to abandoning the hole.
Accordingly, the present invention is directed to overcoming the above noted problems in the art and provides a solution thereto as more particularly described hereinafter.